Various systems and components in a motor vehicle have self-diagnostic capabilities that are useful for identifying and flagging certain events that may deserve subsequent investigation of one or more systems and/or components in order to ascertain if some sort of corrective action may be needed. Occurrence of certain events while a vehicle is in operation may call for more immediate action such as disabling certain accessory systems and/or devices whose operation may be affected by a particular event.
A vehicle's service brake system typically comprises a foot pedal that when depressed by a driver of the vehicle operates service brakes at the vehicle's wheels. A hydraulic brake system is one known type of service brake system. When a driver applies the service brakes, a device, such as a switch, is operated. Operation of the switch typically illuminates the vehicle's stop lamps, but its operation may be a signal that is of interest to other systems and/or devices in the vehicle itself or in a vehicle being towed.
Examples of such switches are electrical pressure switches that are operated by hydraulic fluid pressure when a master cylinder of a hydraulic brake system is operated by a driver depressing the foot pedal, and mechanically-operated electrical switches that are operated by depression of a switch plunger caused by motion of the foot pedal when depressed by the driver.